var string='hello';
var length=string.length;
var string2=string.toUpperCase();
var string3=string2.toLowerCase();

var character=string.charAt(2);
var code=string.charCodeAt(2);
var string=String.fromCharCode(code);
var index=string.indexOf('l');
var reverseIndex=string.lastIndexOf('l');

var array=string.split('l');
var substring1=string.substring(0,index);
var substring2=string.substr(0,index);
var text='world';
var prefix=string+' '
var total=prefix.concat(text);
var substring3=string.slice(0,index);
var substring4=string.slice(index);

var variety=total.replace('l','f');
var change=total.replace(/l/g,'f');
var n=total.search('ll');

let txt='https://www.baidu.com';
let anchor=txt.big().italics().fontcolor('blue').anchor();
let link=txt.fontsize(10).small().bold().link();
let old=txt.fixed().blink().strike();
let top=txt.sup();
let bottom=txt.sub();
